Abstract
Flocculation–flotation is one of the effective methods for addressing the problem of fine-particle flotation. In this study, the hydrophobizing and flotation characteristics of ultrafine sulfide minerals were improved using the polymeric flocculant polyethyleneimine (PEI). The effects of the dosage and molecular weight (Mw) of branched PEI polymers on the flocculation–flotation behavior of sulfide minerals at pH 8.5 were investigated through sedimentation limit measurements. PEI 10,000 and 18,000 g/mol showing the highest efficiency; the optimal concentration was 90 mg/L. In the presence of PEI (10,000 g/mol, 90 mg/L), sodium butyl xanthate (SBX) adsorption increased significantly up to 275–300 mg/L, following the order: CuFeS₂ > PbS > ZnS > FeS₂. Zeta-potential measurements showed increasing negative surface charge with rising pH, strong charge reduction by SBX, and effective charge neutralization by PEI at pH 6–8. Contact angle analysis confirmed that SBX increased mineral hydrophobicity, while FTIR results verified active PEI adsorption on mineral surfaces. Sedimentation kinetics demonstrated that PEI was the main factor accelerating flocculation, whereas SBX contributed through hydrophobic aggregation; their combined use produced a synergistic effect via polymer bridging and hydrophobic interactions. Flotation tests showed that PEI alone improved recovery by 7–10%, while SBX + PEI increased recovery by 17–20% for chalcopyrite and sphalerite, 10–13% for galena, and 9–10% for pyrite, indicating the effectiveness of the combined flocculation–flotation approach for ultrafine sulfide mineral recovery. Consequently, PEI in combination with SBX can be used as a flocculant in the flotation of fine sulfide minerals to enhance their floatability.